Supermicro X7DWU + FreeBSD 10.2 == trouble

So my colo box died a few days ago. I grabbed this spare Supermicro 1U rack box I had sitting around, which is based on a Supermicro X7DWU. I'm running 3x Toshiba 1TB SATA drives in a zfs mirror using FreeBSD 10.2's root-on-ZFS install option, which worked surprisingly well. However, now that the machine is running I'm getting all sorts of odd pauses/hangs, occasionally for more than a minute at a time, with no indicator of what's causing the issues. I did have some odd USB issues in messages, but they were resolved by turning off USB2.0 support in the BIOS. I'm currently running memtest86+ on the machine, but so far it's looking good.

Any suggestions for other things to check? Does anyone have experience with FreeBSD on this particular board?
Some thoughts (in somewhat random order)... You mentioned you are using ZFS on root, but didn't mention how much memory your system has. Maybe try a single disk UFS to rule out ZFS/memory issues. Are there any BIOS updates? You can also try disabling watchdog, hyperthreading, APM, and Plug'n Play (one at a time). Maybe try 10.3-PRE or even go back to 9.3 as a test.
Did you perhaps enable dedup? I've had hangups too when I enabled it on a system that didn't have enough memory.